Communication path distributing units have long been known in the electric wire technology and are often called main distributing frames. In such equipment, it is also known to employ separate adjacent frame sections for terminating cable wires in large numbers on terminal blocks on different horizontal shelves of each unit. The separate sections are employed for cables extending to different types of transmission regions. For example, in a telephone central office, one section might be used for cables extending to the outside plant whereas another section, adjacent to the first, would be used for cables and wires extending to central office equipment. In a similar vein, adjacent frame sections can be employed for terminating wires of external transmission cables in one frame, and wires extending to building equipment or other subscriber locations on another unit.
On the shelves in a section of a distributing frame, the wires usually enter from exposed side or back regions of the shelf after having been passed vertically across the sides or backs of shelves to reach the proper shelf location. Cross-connect jumper wires are then applied to the fronts of the terminal blocks to interconnect the high density terminations. Such jumpers extend from connections on the front of a block, across the front of the block at the upper or lower edge thereof to an intermediate channel between adjacent sections, and to other shelves. The jumpers may also pass to the bottom of the section where they are extended through a jumper wire trough laterally to adjacent frame sections which are similar to that just described. Two examples of wire type distribution frames are to be found in the U.S. Pat. No. 4,002,856 to W. S. Sedlacek et al., and the U.S. Pat. No. 4,320,261 to L. J. Scerbo et al. In another U.S. Pat. No. 4,371,757 to G. DeBortoli et al., the distribution frame is made in the form of a vertical channel through which individual wires are passed to the levels of appropriate apertures or windows, in one wall of the channel. Then the wires are extended through one of the those windows to a terminal block which is removably mounted adjacent to that one window.
In the lightguide fiber technology, there are similar needs for distributing and cross-connecting communication paths and for realizing high density path terminations. However, some frame concepts for the wire technology are not well suited to the fiber technology because the lightguide fibers are relatively fragile in some senses, and they are not conveniently dressed into, or around, small-radius bends. In addition, because the connectorization, i.e., securing fiber to a plug, success rates for lightguide fibers may be less than perfect, it is sometimes necessary to discard fiber ends and associated connector plugs, and attempt a new connection. Fiber slack must be available for use in such events.
Various efforts have been made to achieve high density path terminations and connections in the lightguide technology. A U.S. Pat. No. 4,408,353 to T. P. Bowen et al. shows a communication system employing a so-called splitter, or box, for lightguide fibers in which a cable is brought into a port on one side of the box and the individual fibers thereof are then separately fanned out to different cable connectors at other points in the box. External fiber connections are made at those individual fiber connectors.
A paper by J. Hecht, entitled "Preview of OFC '84 - Single-Frequency Lasers and High-Speed System Developments Highlight the New Orleans Meeting", and appearing at pages 69-85 of Lasers & Applications, January 1984, shows at pages 78 and 81 a splice loop unit for use in a lightguide wiring center for local area networks. The unit includes an array of pairs of fiber-coil-receiving pockets. Two fibers which are to be connected together are extended along opposite sides of the splice loop unit to a free pair of pockets, and then each fiber is extended upwardly so the two fibers can be connected above the unit. The slack in each fiber is dropped into a different pocket of the pair, and the connector is placed in a slot between the two pockets of the pair.
A different approach to the lightguide fiber distribution and interconnecting problem is shown in a paper by M. R. Gotthardt entitled "Bell System Lightguide Cable Interconnection Equipment, Central Office to Customer Premises" and appearing at pages 45-48 of Proceedings of 32nd International Wire and Cable Symposium at Cherry Hill, N.J., Nov. 15-17, 1983. Single-frame installation arrangements are shown. In one of these arrangements, for example, a lightguide fanout unit is equipped with a front panel having fiber connectors mounted thereon and each extending from the outside to the inside of the fanout unit. That unit is also equipped with a ribbon of fibers which extends from respective inner ends of the connectors through an aperture in a wall of the unit to a fiber array connector on the outside of the unit. Multifiber ribbon-based external lightguide cables coming to a frame, or equipment box, employing the fanout unit are brought into the box and their ribbons are interconnected to the fanout unit by means of a fiber array connector in the overall equipment frame. Relatively permanently installed outside plant cable fibers and relatively changeably installed interconnect jumpers share space to the extent that when a jumper connection is changed at least one associated outside plant cable fiber is likely to be disturbed. This poses risks to cable fiber mechanical integrity as will be subsequently discussed.